[std/channels]fix recv leaks(Part One) (#17394)

tests/stdlib/tchannels_pthread.nim

@@ -89,6 +89,7 @@ proc runSuite(
         capacity(chan) == 1
         isBuffered(chan) == false
         isUnbuffered(chan) == true
+
     else:
       chan = allocChannel(size = int.sizeof.int, n = 7)
       check:
@@ -109,7 +110,7 @@ proc runSuite(
       discard pthread_join(threads[0], nil)
       discard pthread_join(threads[1], nil)
 
-      freeChannel(chan)
+    freeChannel(chan)
 
 # ----------------------------------------------------------------------------------
 

tests/stdlib/tchannels_simple.nim

@@ -24,8 +24,7 @@ var worker1: Thread[void]
 createThread(worker1, firstWorker)
 
 # Block until the message arrives, then print it out.
-var dest = ""
-chan.recv(dest)
+let dest = chan.recv()
 doAssert dest == "Hello World!"
 
 # Wait for the thread to exit before moving on to the next example.